The present invention relates to a clamping device for the releasable fastening of a part on a shaft, a clamping nut which can be screwed onto the shaft being provided for clamping the part in place.
EP 0 480 163 A1, for example, has disclosed a quick-clamping device, in particular for fastening disk-shaped tools to a drive spindle of a powered hand tool. The quick-clamping device has a nut, with pressure plate axially supported thereon, and a hand-screw part enclosing the nut and the pressure plate, the nut and the hand-screw part forming an annular space in between, in which spherical rolling bodies are contained, these rolling bodies bearing against surfaces of these three elements and rolling there on longitudinal paths. The surfaces of the hand-screw part are symmetrical to one another, so that approximately axially parallel contact points are obtained there, whereas the track of the supporting surface of the nut lies on a larger circumferential circle than the opposite track of the pressure plate, as a result of which a rotary movement is transmitted to the nut when the hand-screw part is rotated and the pressure plate is fixed. Manual actuation for fastening a disk-shaped tool to a powered hand tool, or for releasing said disk-shaped tool, is thus possible without a tool.
The satisfactory symmetrical arrangement of said surfaces relative to one another is necessary for satisfactory operation of this quick-clamping device. Additional sealing rings which are intended to prevent the ingress of contaminants or foreign substances into the space defined by the surfaces are provided. Furthermore, the pressure plate must be satisfactorily oriented relative to the nut and guided in a movable manner, so that the desired rolling conditions are ensured. Furthermore, the possibility of the hand-screw part striking, for example, the workpiece to be machined during the operation of the powered hand tool cannot be ruled out, in the course of which undesirable rotation of the hand-screw part may occur, which leads to relief of the clamped grinding wheel and thus to unintentional release of the grinding wheel.
The object of the present invention is therefore to specify a clamping device according to the features of the preamble of claim 1 in which these disadvantages are eliminated.
According to the invention, this object is achieved in that a chamber is provided between a pressure member for bearing against the part and the clamping nut, this chamber containing a hydraulic pressure medium, an escape space which can be connected to the chamber being provided for the hydraulic pressure medium. When the escape space is connected, the clamping pressure is removed from the grinding wheel at least to such an extent that release of the clamping nut by hand is possible without additional auxiliary tools. The clamping force is directed into the clamping nut by the pressure member via the hydraulic pressure medium. The pressure in the hydraulic pressure medium, under the effective clamping force, is increased relative to the atmospheric pressure.
The clamping device according to the invention has considerable advantages over the known clamping device. No surfaces on which balls can roll have to be machined; no special measures need be taken in order to ensure that the parts having these surfaces are positioned relative to one another in a highly precise manner.
If the clamping device according to the invention is used, for example, in an angle grinder, the grinding wheel is clamped in place between a counterholder and the clamping device according to the invention. During the operation of such angle grinders, the clamping nut normally tightens automatically, so that the grinding wheel is firmly clamped in place between the counterholder and the pressure member of the clamping device according to the invention. The clamping force is directed into the clamping nut via the hydraulic pressure medium, the clamping nut transmitting this clamping force via the screwed connection into the screw spindle of the angle grinder. If the grinding wheel is now to be removed, no separate tool is required in order to release the clamping device according to the invention from the screw spindle. The escape space is merely connected to the chamber in which the hydraulic pressure medium is arranged under pressure. The hydraulic pressure medium, under the pressure inherent in it, now escapes into the escape space, the pressure in the hydraulic pressure medium being rapidly reduced on account of the increase in volume of the chamber. After the pressure reduction has been effected, the pressure member and consequently also the grinding wheel are relieved to such an extent that manual unscrewing of the clamping nut or of the clamping device according to the invention is possible without any problems.
The hydraulic pressure medium used may be, for example, hydraulic oil or also an easily deformable, at least approximately incompressible solid, a hydraulic oil probably being advantageous for many applications.
The escape space is preferably cleared or blocked by a closure member, in which case a slide, for example, may be used for this purpose, this slide being arranged between chamber and escape space and producing the connection between chamber and escape space after it has been actuated. An advantageous development according to the invention provides a driving piston as closure member, this driving piston being arranged in the escape space in a longitudinally displaceable manner and, depending on the position selected, clearing or blocking the escape space. The escape space may then be described as the space which the piston displaces or clears during the piston travel.
The chamber for accommodating the hydraulic pressure medium may be sealed off by suitable seals. However, a development according to the invention provides for the hydraulic pressure medium to be arranged in a flexible closed envelope which is impermeable to the hydraulic pressure medium. The envelope filled with the hydraulic pressure mediumxe2x80x94for example silicone oilxe2x80x94is merely inserted into the chamber, so that no further sealing devices are necessary. The envelope is made in such a way that it can follow deflections of the pressure member and of the closure member. The envelope is preferably designed as an annular body which can be put onto the shaft.
The pressure member preferably has an, in particular annular, load piston which is arranged on the shaft in a longitudinally displaceable manner and defines the chamber. The load piston can retract in the direction of the chamber when the hydraulic pressure medium escapes into the escape space. The load piston, with its one front end, can load, for example, the grinding wheel.
The driving piston (already mentioned) of the closure member defines the escape space. The load piston and the driving piston are preferably arranged in recesses of the clamping nut in a longitudinally displaceable manner, in which case the clamping nut, with its walls defining these recesses, defines the chamber and/or the escape space. This development according to the invention is especially space-saving, since the chamber for accommodating the hydraulic pressure medium and said escape space can be integrated in the clamping nut in a simple manner.
The load piston and the driving piston each have a piston area which can be acted upon by the hydraulic pressure medium, the piston area of the load piston being greater than the piston area of the driving piston. The smaller the piston area of the driving piston, the smaller the force which acts on the driving piston from the hydraulic pressure medium under high pressure when the driving piston blocks the escape space. In the clamping device according to the invention, the escape space is designed for accommodating as much hydraulic pressure medium as required for at least partly removing the clamping pressure from the clamping disk. Depending on the design of the individual components, a displacement travel of approximately just {fraction (3/10)} mm of the pressure member may be sufficient in order to relieve the clamping disk for manual release of the clamping nut. This means that the displacement travel of the driving piston relative to the displacement travel of the load piston behave in inverse proportion to the ratio of the piston areas of the driving piston and load piston.
So that the closure member reliably blocks the escape space, a holding device is preferably provided, this holding device holding the driving piston in the position in which the escape space is blocked. This holding device may have a pushbutton and locking bodies, the pushbutton holding the locking bodies between the driving piston and a stop. Under the pressure force of the hydraulic pressure medium, the driving piston is pressed via the locking bodies against the stop and is satisfactorily supported on the stop. This stop may be formed, for example, directly on the clamping nut; however, it may also be formed by an angled flange of a sheet-metal sleeve which is pressed into a bore of the clamping nut.
The holding device referred to is designed in such a way that the depressed pushbutton opens a clearance space for accommodating the locking bodies. Under the pressure force, acting on the driving piston, of the hydraulic pressure medium, the locking bodies are pressed into this clearance space, the driving piston now being run directly against the stop. In this situation, the escape space is completely cleared, so that the escape space is connected to the chamber. The displacement of the locking bodiesxe2x80x94which are preferably formed by ballsxe2x80x94into the clearance space is preferably assisted by a sloping surface which is formed on a front end of the driving piston. When the pushbutton is in its initial positionxe2x80x94that is when the pushbutton is not depressedxe2x80x94the locking bodies are supported on a supporting surface of the pushbutton. This supporting surface may be formed, for example, by the cylindrical lateral surface of the pushbutton. The sloping surface already mentioned and provided on the driving piston is preferably arranged at an oblique angle to this supporting surface and at an oblique angle to the stop. This means that the locking bodies, preferably the balls, are clamped in place between the driving piston, the pushbutton and the stop, which is preferably formed on the clamping nut. The supporting surface and the stop surface are preferably arranged at right angles to one another. The sloping surface is inclined in the direction of the clearance space for accommodating the locking bodies. The clearance space is preferably formed by a circumferential groove which is formed on the pushbutton and is axially adjacent to the supporting surface.
If the driving piston blocks the escape space, the locking bodies, preferably designed as balls, are supported on the sloping surface of the driving piston, the stop surface of the stop, and the supporting surface of the pushbutton. The position and magnitude of the resulting force which is transmitted between the supporting surface and the ball depends on the inclination of the sloping surface. This resulting force may in turn be represented by two equivalent forces which are at right angles to one another, one of which is arranged perpendicularly to the supporting surface of the pushbutton and the other of which is arranged perpendicularly to the stop surface of the stop. The inclination of the sloping surface therefore establishes the magnitude of the equivalent force acting on the supporting surface. For simple operation of the pushbutton, it is advisable for the equivalent force acting on the supporting surface to be kept so small that it is possible to depress the pushbutton without any problems. The more acute the angle of inclination between the sloping surface and the longitudinal axis of the driving piston, the greater is the equivalent force which acts on the supporting surface of the pushbutton.
The pushbutton is preferably moved into its initial position under spring deflection by the force of a spring. The pushbutton can be arranged in a radially or axially directed recess of preferably the clamping nut, that is to say it can be displaced radially or axially.